— 346 Mesozore Rocks of Sinan. 
Petroleum Research has thus been in the first place to re-study the 
great north-east-south-west fold of Maghara, etc., in which the 
Jurassic and Lower Cretaceous strata are best developed, and 
to prove the extension of these strata to the eastward in the Risan el 
Aneiza hills. Further, it has enabled the writers to become 
personally acquainted with the trend of the researches already under- 
taken, enabling them to attack the problems awaiting solution with 
enhanced knowledge. 
There remains, however, a main question which will have occurred 
to most geologists and demands an answer. Why are these formations 
so strongly developed in the Maghara fold, yet so strikingly absent 
further south where Cenomanian strata of the most typical kind 
overlie a great thickness of Nubian Sandstone, in which no trace 
of fossiliferous formations are to be met with ? 
We believe the answer to be that we are dealing with the 
phenomenon of lateral variation on the large scale. To the south ot 
this region lay a great granitic-metamorphic continent. As its 
borders were approached, the strata became more and more sandy, 
further away from it marine formations were developed at an earlier 
age than further to the south. The theme dealt with by the writer 
in his paper on the “Secular Oscillations”, read before the 
Geological Society, has expanded (W. Fs Hume, “ Secular 
Oscillation in Egypt during the Cretaceous and Hocene periods, ’ 
Q.J.G.S8., vol. lxvii, 1911, pp. 118-48). We can no longer speak of 
the “ Nubian Sandstone ”’ as of Cretaceous age ; it is a lithological 
condition which, beginning in late Carboniferous times both in 
Sinai and Eastern Egypt, was developed in Northern Sinai during 
the Trias and Lias, and also alternating with the fossiliferous 
Jurassic strata, as may be well seen in ascending the main Maghara 
crest. If these beds of known date were not present, it would be 
impossible to distinguish the sandstones from those regarded as of 
typically “‘ Nubian Sandstone ”’ character elsewhere. 
The writer did not himself nete so marked an alteration in the 
Lower Cretaceous formations. For Egypt itself he has already 
directed attention in the above paper to the breaking up of the 
Upper Cretaceous series by “ Nubian” Sandstones, these lying 
very markedly between strata of Cenomanian and Turonian age ; 
whereas south of that latitude both the fossiliferous Cenomanian 
and Turonian strata are represented by sandstone alone. We there- 
fore scarcely expect, in pursuing the research further, to find 
fossiliferous Jurassic and Lower Cretaceous strata south of the fold 
in which they are at present known, but rather that elsewhere they 
will be ‘‘ Nubian Sandstone”. Much light has been thrown by 
Messrs. Moon and Sadek’s work on the structure of the north-western 
portion of North Sinai, which embraces this area. M. Barthoux had 
already noted that the area was folded, constituting a series of 
1 See Ball on the ‘‘ Geography and Geology of West Central Sinai’, reviewed 
in GEOL. Maca., 1917, p. 80. 
